When it comes to farmland in Maine, not all soils are equal. Some are prime, some are important, some are unique and some are not worthy of any rating. It’s all based on a soil’s ability and capacity to produce quality food or fiber crops.
What soil falls into which category is determined by the United States Department of Agriculture’s Natural Resource Conservation Service. According to the USDA’s 2020 state agriculture review, Maine has 1.3 million acres of farmland and all of it falls into one of the soil categories.
“There are lots of reasons to care about this,” Tony Jenkins, Maine USDA state soil scientist, said. “Soil is central to food and fiber production and it’s also important information to know for development purposes.”
According to the USDA criteria, prime farmland is soil that has the best physical and chemical characteristics to produce food, animal feed and forage crops. It’s also the best in terms of pasture and forest. It gets the optimum amount of rain or has access to irrigation and is not highly erodible.
Unique farmland, according to the USDA, is land that can be used for the production of specific, high-value food and fiber crops. It has a special combination of soil quality, growing season, moisture supply, temperature, humidity and elevation to grow and sustain those crops.
Farmland that does not fall into prime or unique categories is considered to be of statewide importance for the production of crops. This is land that almost meets the criteria for prime farmland.
“A good way to think about what makes a certain soil prime or not is to think about what rules it out,” according to Dr. Susan Erich, professor of plant and soil chemistry at the University of Maine. “It’s looking at it as why you would not want to plant anything there.”
Sometimes what makes a soil prime farmland rather than a lower designation is all about location, Erich said.
“If the soil is located on a steep slope or merging into a wetland and is poorly drained, it won’t be considered prime or even important farmland,” Erich said. “In some areas covered by trees, you could cut the trees down and it’s possible to turn the land into a farm, but there is not much you can do to convert poorly drained or steep slopes into a productive field.”
Soils in Maine were mapped out at the county level starting in the 1950s and, according to Jenkins, the final acre was completed in 2011.
The information from those soil surveys is readily available from county Maine Soil Conservation Service offices.
“Those maps have a whole bunch of data on properties of the soil, whether its sand, silt or clay, if it’s really stoney, how deep they go and what the soil chemistry looks like,” said Eric Giberson, district conservationist in the Fort Kent soil conservation field office. “The designations for the soils all come down to its ability to produce.”
Over the years the farmland designations have also been used as criteria for awarding grants, protecting areas from commercial or residential development, zoning and to preserve farmland.
“When making those decisions, knowing the designation of the soils adds weight to the arguments,” Giberson said.
In geologic terms, Maine soils are fairly young, according to Erich. They formed after the last glaciers receded from the area around 10,000 years ago. Since then, the soils have been slowly adding layers while environmental conditions change their chemistry.
Those changes are ongoing, Erich said, and with climate change the soils in Maine are bound to change. But today’s farmers and homesteaders should not worry their prime or important farmland is going to get knocked down a level anytime soon.
“Soils are not a static system,” Erich said. “We have seen Maine’s average rainfall increase and temperatures warming, so the soils will change, but they are not changes we will see in our lifetimes.”